In recent years, with the multimediatization of information in mobile communication systems, transmitting high capacity data such as still images and movies in addition to speech data has become popular. To realize the transmission of high capacity data, a technology in which a high-frequency radio band is used to provide a high transmission rate is studied actively.
However, when a high-frequency radio band is used, although a high transmission rate can be expected in a short distance, attenuation due to transmission distance becomes greater as the distance increases. Accordingly, when the mobile communication system employing a high-frequency radio band is operated, the coverage area of a radio communication base station apparatus (hereinafter “base station”) becomes small, which requires that a larger number of base stations be set up in order to prevent the service area from reducing. Since the set-up of base stations involves large costs, a technology is strongly demanded for realizing communication services which employ a high-frequency radio band and preventing an increase in the number of base stations.
To meet this demand, to expand the coverage area of the base stations, relay transmission technologies are investigated in which a radio communication relay station apparatus (hereinafter “relay station”) is set up between a radio communication mobile station apparatus (hereinafter “mobile station”) and a base station, and in which communication between the mobile station and the base station is carried out via the relay station.
Meanwhile, in future mobile communication systems, combining various radio access technologies (RATs) such as W-CDMA (Wideband Code Division Multiple Access), LTE (long-term evolution), WLAN (Wireless LAN), and WiMAX (Worldwide Interoperability for Microwave Access) and overlapping a plurality of RAT coverage areas in the service area of mobile communication will be taken into consideration. Then, in these mobile communication systems, a mobile station needs to detect in which RAT coverage area the mobile station is currently located and what communication service the mobile station is enjoyable. For example, when part of an LTE coverage area includes a WLAN coverage area, a mobile station located in the WLAN coverage area does not enjoy a WLAN communication service unless the mobile station detects that the mobile station is located in the WLAN coverage area, and the mobile station enjoys an LTE communication service only.
Then, conventionally, Non-Patent Document 1 discloses a technique of detecting in which RAT coverage area the mobile stations are located by reporting another RAT's information (e.g. WLAN) to the mobile stations from a RAT's base station (e.g. LTE) based on location information of the mobile stations.    Non-Patent Document 1: 3GPP TS 25.331 V5.19.0 (2006-12); Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 5)